Transducers convert signals from one domain to another and are often used in sensors. One common sensor with a transducer that is seen in everyday life is a microphone that converts sound waves to electrical signals.
Microelectromechanical system (MEMS) based sensors include a family of transducers produced using micromachining techniques. MEMS, such as a MEMS microphone, gather information from the environment by measuring the change of physical state in the transducer and transferring the signal to be processed by the electronics which are connected to the MEMS sensor. MEMS devices may be manufactured using micromachining fabrication techniques similar to those used for integrated circuits.
MEMS devices may be designed to function as oscillators, resonators, accelerometers, gyroscopes, pressure sensors, microphones, micro-mirrors, etc. Many MEMS devices use capacitive sensing techniques for transducing the physical phenomenon into electrical signals. In such applications, the capacitance change in the sensor is converted to a voltage signal using interface circuits.
For example, a capacitive MEMS microphone includes a backplate electrode and a membrane arranged in parallel with the backplate electrode. The backplate electrode and the membrane form a parallel plate capacitor. The backplate electrode and the membrane are supported by a support structure arranged on a substrate.
The capacitive MEMS microphone is able to transduce sound pressure waves, for example speech, at the membrane arranged in parallel with the backplate electrode. The backplate electrode is perforated such that sound pressure waves pass through the backplate while causing the membrane to vibrate due to a pressure difference formed across the membrane. Hence, the air gap between the membrane and the backplate electrode varies with vibrations of the membrane. The variation of the membrane in relation to the backplate electrode causes variation in the capacitance between the membrane and the backplate electrode. This variation in the capacitance is transformed into an output signal responsive to the movement of the membrane and forms a transduced signal.
One characteristic of a MEMS device is the robustness of the MEMS device. For example, a capacitive MEMS microphone has a characteristic robustness which determines the magnitude of shock or impact the MEMS microphone can withstand without damage. Often, the membrane, which is deflectable, is more prone to fracture or failure from shock or impact than other portions of the MEMS microphone.